1961 to 1970
Overview
Manufacturer	Jaguar Cars
Production	1961–1970 13,382 3.8 Litre 5,137 4.2 Litre 5,763 420G
Assembly	Coventry, England
Body and chassis
Class	Full-size luxury car
Body style	4-door saloon
Layout	FR layout
Related	Daimler DS420
Powertrain
Engine	3781 cc XK I6 to 1964 4235 cc XK I6
Dimensions
Wheelbase	120 in (3,000 mm)
Length	202 in (5,100 mm)
Width	76.3 in(1,938 mm)
Height	54.5 in (1,380 mm)
Curb weight	4,200 lb (1,900 kg)

 The Jaguar Mark X (Mark ten) was the top-of-the-range saloon car built by the British manufacturer Jaguar, primarily aimed at the United States market. The Mark X succeeded the Mark IX as the company's largest saloon model.

Body

saloon; doors: 4; seats: 6; front seat: double.

During development, the unitary construction body-shell was dubbed "Zenith," and the DS 420 Limousine used this floor pan long after the Mark X was discontinued. The Mark X was the first car to feature the new layout, which had four headlamps set into rounded front fenders with a vaned grill. The dashboard, window trim, a pair of enormous bookmatched fold out rear picnic tables, and a front seat pull-out picnic table stowed beneath the instrument cluster were all standard woodwork on the penultimate Jaguar. Later options included air conditioning and a sound-proof glass partition between the front and rear seats.

From its introduction until the arrival in 1992 of the low-slung XJ220, the Mark X stood as one of the widest production Jaguars ever built. Asked in 1972 if he thought the Mark X had grown rather too large, Jaguar chairman William Lyons, agreed that it "definitely" had: he opined that the then recently introduced and notably more compact Jaguar XJ6 was, by contrast an "ideal size".

The substantial doors required helical torsion springs inside the door pillars to enable them to be opened from the inside with an acceptably low level of effort.

Mechanical

PERFORMANCE ENGINE 3.8-litre

• FUEL CONSUMPTION: 17.1 m/imp gal, 14.2 m US gal, 16.5 1 x 100 km
• MAX SPEED: 120 mph, 193.2 km h
• max speed in 1st gear: 37.9 mph, 61 km/h
• max speed in 2nd gear: 68.9 mph, 111 km/h
• max speed in 3rd gear: 99.4 mph, 160 km/h
• max speed in 4th gear: 120 mph, 193.2 km/h
• power-weight ratio: 15.2 lb/hp, 6.9 kg/hp
• useful load: 1058 1b, 480 kg

The Mark X was the first Jaguar saloon to feature independent rear suspension. It differed from earlier large Jaguar saloons in having 14" wheels instead of the more common 15". It used a wider-track version of Jaguar's IRS unit first seen on the E Type, which was subsequently used on Jaguar vehicles until XJ-S production ended in 1996. Front suspension used double wishbones with coil springs and telescopic dampers. The car initially featured a 3781 cc version of Jaguar's XK in-line six-cylinder engine. A 9:1 compression ratio was standard, but an alternative 8:1 compression ratio was available as an option. For the London Motor Show in October 1964 the enlarged 4,235 cc unit took over, although the 3.8-litre unit could still be specified until October 1965. Triple SU carburettors were fitted, fed from an AC Delco air filter mounted ahead of the right hand front wheel.

PERFORMANCE ENGINE 4.2-litre
Engine Capacity 258.43 cu in, 4,234.89 cu cm
Fuel Consumption 17.1 m/imp gal, 14.2 m/US gal, 16.5 1 x 100 km
Max Speed 120 mph, 193.2 km/h
max power (DIN): 265 hp at 5,400 rpm
max torque (DIN): 283 1b ft, 39.1 kg m at 4,000 rpm
max number of engine rpm: 6,000
specific power: 62.6 hp/l

Transmission options were manual, manual with overdrive, automatic or automatic with overdrive. The arrival of the 4.2-litre power unit coincided with the introduction of a newly developed all-synchromesh four-speed gear box replacing the venerable box inherited by the 3.8-litre Mark X from the Mark IX which had featured synchromesh only on the top three ratios Many domestic market cars and almost all cars destined for the important North American markets left the factory with a Borg Warner automatic gear-box. The 4.2-litre engine's introduction was also marked by a transmission upgrade for buyers of the automatic cars, who saw the Borg Warner transmission system switched from a DG to a Typ-8 unit. The power train was completed by a Thornton Powr-Lok limited-slip differential. Stopping power for this heavy car came from power-assisted disc-brakes on all four wheels.Power-assisted steering was standard, the later 4.2 cars receiving Adwest Varamatic variable ratio steering boxes.

VARIATIONS AND OPTIONAL ACCESSORIES:

4-speed mechanical gear box and Laycock-de Normanville overdrive in IV (1 3.377, II 1.859, III 1.284, IV I -ov. 0.777), multiplication ratio 0.778, max speed 120 mph, 193.2 km/h, axle ratio 3.77 : 1

Borg-Warner automatic gearbox, hydraulic torque convertor and planetary gears with 3 ratios (I 2.305, II 1.435, III 1), max ratio of convertor at stall 2.15.

420G

For the London Motor Show in October 1966 the Mark X was renamed the Jaguar 420G (not to be confused with the smaller Jaguar 420). The 420G was distinct from the Mark X only with the addition of a vertical central bar splitting the grille in two, side indicator repeaters on the front wings, and a chrome strip along the wing and door panels (two tone paint schemes were also available with the chrome strip omitted). Interior changes included perforations in the central sections of the leather seats, padded dashboard sections for safety, moving the clock to a central position, and the introduction of air conditioning as an option.

A "limousine" version was available, on the standard wheelbase, with a dividing glass screen partition and front bench seat replacing the separate seats of standard cars. The wheelbase was extended by 21" with the mechanical underpinnings of the car being subtly re-bodied for the 1968 Daimler DS420. This car was built until 1992 and used by many countries in official capacities, and frequently by funeral homes; either with a saloon body for carrying mourners or a hearse body.

Despite running for the same length of time as the Mark X (5 years) the 420G sold in less than a third of the numbers: this lack of popularity and the increasing production of the XJ6 resulted in the 420G being run out of production in 1970.